Hvac

If anyone knows -

Does heated engine coolant constantly run through the heater core in these trucks (99 and newer).

Or is there a valve in the supply or return coolant lines or even at the heater core itself, that stops the flow of heated engine coolant if the temp knob is not calling for heat, like the old days.

Thanks for any help.

let me put it this way:
heater core inlets are directly going through the firewall.
heater core hoses are directly connected to the heater core inlets inside the engine bay
there are no vlaves or such anywhere on the hoses, they go straight into the pump/core.
ther a ppear to be no vlaves on the heater core of any nature.
i have just checked.
haynes does not mention/picture any valves.
if it's blowing hor with climate control on cold, probabaly your climate control unit. appears to be all electrically controlled, most likely - electric actuators, maybe vaccum though i doubt, on ducts doors.

Thanks for the info.

I have a hard time understanding that there is always 190 deg fluid running inside the truck.

Is the excess heat vented to the outside?

Thanks for the info.

I have a hard time understanding that there is always 190 deg fluid running inside the truck.

Is the excess heat vented to the outside?

i donno.

also, if you read my post, i did not say there is no valve. what i was saying was - there is none in the engine bay very obviously and, considering that you can see heater core pipes sticking out of the firewall (see for yourself, 2 parallell hoses running into the firewall about upper midengine level pass side ) - there's no way to put a valve on the core side either. haynes pictures of the core removal show no signs of any valve.

honestly, o like it better this way, as from previous experince with that valve on buick, i'd rather have it not. leaks.

pretty much, if you have hot air running with setting on cold, it's the door actuator or climate control unit itself, as it all appears to be elctronics.

If anyone knows -

Does heated engine coolant constantly run through the heater core in these trucks (99 and newer).

Or is there a valve in the supply or return coolant lines or even at the heater core itself, that stops the flow of heated engine coolant if the temp knob is not calling for heat, like the old days.

Thanks for any help.

YES, coolant is always circulating thru the front heater core. Subs and Tahoes with rear HVAC may have a valve installed for the rear system.

Temp is controlled by the "temp control door" which allows air to flow thru the heater core into the cab. In the "cold" position no air flows thru the heater core.

Are you having issues that you have not described??